1 /*
2 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import java.io.*;
28 import java.util.*;
29
30 /**
31 * The {@code Throwable} class is the superclass of all errors and
32 * exceptions in the Java language. Only objects that are instances of this
33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
34 * can be thrown by the Java {@code throw} statement. Similarly, only
35 * this class or one of its subclasses can be the argument type in a
36 * {@code catch} clause.
37 *
38 * For the purposes of compile-time checking of exceptions, {@code
39 * Throwable} and any subclass of {@code Throwable} that is not also a
40 * subclass of either {@link RuntimeException} or {@link Error} are
41 * regarded as checked exceptions.
42 *
43 * <p>Instances of two subclasses, {@link java.lang.Error} and
44 * {@link java.lang.Exception}, are conventionally used to indicate
45 * that exceptional situations have occurred. Typically, these instances
46 * are freshly created in the context of the exceptional situation so
47 * as to include relevant information (such as stack trace data).
48 *
49 * <p>A throwable contains a snapshot of the execution stack of its thread at
50 * the time it was created. It can also contain a message string that gives
51 * more information about the error. Finally, it can contain a <i>cause</i>:
52 * another throwable that caused this throwable to get thrown. The cause
53 * facility is new in release 1.4. It is also known as the <i>chained
54 * exception</i> facility, as the cause can, itself, have a cause, and so on,
55 * leading to a "chain" of exceptions, each caused by another.
56 *
57 * <p>One reason that a throwable may have a cause is that the class that
58 * throws it is built atop a lower layered abstraction, and an operation on
59 * the upper layer fails due to a failure in the lower layer. It would be bad
60 * design to let the throwable thrown by the lower layer propagate outward, as
61 * it is generally unrelated to the abstraction provided by the upper layer.
62 * Further, doing so would tie the API of the upper layer to the details of
63 * its implementation, assuming the lower layer's exception was a checked
64 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
65 * cause) allows the upper layer to communicate the details of the failure to
66 * its caller without incurring either of these shortcomings. It preserves
67 * the flexibility to change the implementation of the upper layer without
68 * changing its API (in particular, the set of exceptions thrown by its
69 * methods).
70 *
71 * <p>A second reason that a throwable may have a cause is that the method
72 * that throws it must conform to a general-purpose interface that does not
73 * permit the method to throw the cause directly. For example, suppose
74 * a persistent collection conforms to the {@link java.util.Collection
75 * Collection} interface, and that its persistence is implemented atop
76 * {@code java.io}. Suppose the internals of the {@code add} method
77 * can throw an {@link java.io.IOException IOException}. The implementation
78 * can communicate the details of the {@code IOException} to its caller
79 * while conforming to the {@code Collection} interface by wrapping the
80 * {@code IOException} in an appropriate unchecked exception. (The
81 * specification for the persistent collection should indicate that it is
82 * capable of throwing such exceptions.)
83 *
84 * <p>A cause can be associated with a throwable in two ways: via a
85 * constructor that takes the cause as an argument, or via the
86 * {@link #initCause(Throwable)} method. New throwable classes that
87 * wish to allow causes to be associated with them should provide constructors
88 * that take a cause and delegate (perhaps indirectly) to one of the
89 * {@code Throwable} constructors that takes a cause. For example:
90 * <pre>
91 * try {
92 * lowLevelOp();
93 * } catch (LowLevelException le) {
94 * throw new HighLevelException(le); // Chaining-aware constructor
95 * }
96 * </pre>
97 * Because the {@code initCause} method is public, it allows a cause to be
98 * associated with any throwable, even a "legacy throwable" whose
99 * implementation predates the addition of the exception chaining mechanism to
100 * {@code Throwable}. For example:
101 * <pre>
102 * try {
103 * lowLevelOp();
104 * } catch (LowLevelException le) {
105 * throw (HighLevelException)
106 * new HighLevelException().initCause(le); // Legacy constructor
107 * }
108 * </pre>
109 *
110 * <p>Prior to release 1.4, there were many throwables that had their own
111 * non-standard exception chaining mechanisms (
112 * {@link ExceptionInInitializerError}, {@link ClassNotFoundException},
113 * {@link java.lang.reflect.UndeclaredThrowableException},
114 * {@link java.lang.reflect.InvocationTargetException},
115 * {@link java.io.WriteAbortedException},
116 * {@link java.security.PrivilegedActionException},
117 * {@link java.awt.print.PrinterIOException},
118 * {@link java.rmi.RemoteException} and
119 * {@link javax.naming.NamingException}).
120 * All of these throwables have been retrofitted to
121 * use the standard exception chaining mechanism, while continuing to
122 * implement their "legacy" chaining mechanisms for compatibility.
123 *
124 * <p>Further, as of release 1.4, many general purpose {@code Throwable}
125 * classes (for example {@link Exception}, {@link RuntimeException},
126 * {@link Error}) have been retrofitted with constructors that take
127 * a cause. This was not strictly necessary, due to the existence of the
128 * {@code initCause} method, but it is more convenient and expressive to
129 * delegate to a constructor that takes a cause.
130 *
131 * <p>By convention, class {@code Throwable} and its subclasses have two
132 * constructors, one that takes no arguments and one that takes a
133 * {@code String} argument that can be used to produce a detail message.
134 * Further, those subclasses that might likely have a cause associated with
135 * them should have two more constructors, one that takes a
136 * {@code Throwable} (the cause), and one that takes a
137 * {@code String} (the detail message) and a {@code Throwable} (the
138 * cause).
139 *
140 * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method,
141 * which allows programmatic access to the stack trace information that was
142 * previously available only in text form, via the various forms of the
143 * {@link #printStackTrace()} method. This information has been added to the
144 * <i>serialized representation</i> of this class so {@code getStackTrace}
145 * and {@code printStackTrace} will operate properly on a throwable that
146 * was obtained by deserialization.
147 *
148 * @author unascribed
149 * @author Josh Bloch (Added exception chaining and programmatic access to
150 * stack trace in 1.4.)
151 * @jls3 11.2 Compile-Time Checking of Exceptions
152 * @since JDK1.0
153 */
154 public class Throwable implements Serializable {
155 /** use serialVersionUID from JDK 1.0.2 for interoperability */
156 private static final long serialVersionUID = -3042686055658047285L;
157
158 /**
159 * Native code saves some indication of the stack backtrace in this slot.
160 */
161 private transient Object backtrace;
162
163 /**
164 * Specific details about the Throwable. For example, for
165 * {@code FileNotFoundException}, this contains the name of
166 * the file that could not be found.
167 *
168 * @serial
169 */
170 private String detailMessage;
171
172 /**
173 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
174 * stack trace} to a one-element array containing this sentinel
175 * value indicates future attempts to set the stack trace will be
176 * ignored. The sentinal is equal to the result of calling:<br>
177 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
178 */
179 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
180 new StackTraceElement("", "", null, Integer.MIN_VALUE);
181
182 /**
183 * Sentinel value used in the serial form to indicate an immutable
184 * stack trace.
185 */
186 private static final StackTraceElement[] STACK_TRACE_SENTINEL = initStackTraceSentinel();
187
188 private static StackTraceElement[] initStackTraceSentinel() {
189 StackTraceElement[] ste = new StackTraceElement[1];
190 ste[0] = STACK_TRACE_ELEMENT_SENTINEL;
191 return ste;
192 }
193
194 /**
195 * A value indicating the stack trace field has not yet been initialized.
196 */
197 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0];
198
199 /*
200 * To allow Throwable objects to be made immutable and safely
201 * reused by the JVM, such as OutOfMemoryErrors, the three fields
202 * of Throwable that are writable in response to user actions,
203 * cause, stackTrace, and suppressedExceptions obey the following
204 * protocol:
205 *
206 * 1) The fields are initialized to a non-null sentinel value
207 * which indicates the value has logically not been set.
208 *
209 * 2) Writing a null to the field indicates further writes
210 * are forbidden
211 *
212 * 3) The sentinel value may be replaced with another non-null
213 * value.
214 *
215 * For example, implementations of the HotSpot JVM have
216 * preallocated OutOfMemoryError objects to provide for better
217 * diagnosability of that situation. These objects are created
218 * without calling the constructor for that class and the fields
219 * in question are initialized to null. To support this
220 * capability, any new fields added to Throwable that require
221 * being initialized to a non-null value require a coordinated JVM
222 * change.
223 */
224
225 /**
226 * The throwable that caused this throwable to get thrown, or null if this
227 * throwable was not caused by another throwable, or if the causative
228 * throwable is unknown. If this field is equal to this throwable itself,
229 * it indicates that the cause of this throwable has not yet been
230 * initialized.
231 *
232 * @serial
233 * @since 1.4
234 */
235 private Throwable cause = this;
236
237 /**
238 * The stack trace, as returned by {@link #getStackTrace()}.
239 *
240 * @serial
241 * @since 1.4
242 */
243 private StackTraceElement[] stackTrace = EMPTY_STACK;
244
245 // Setting this static field introduces an acceptable
246 // initialization dependency on a few java.util classes.
247 private static final List<Throwable> suppressedSentinel =
248 Collections.unmodifiableList(new ArrayList<Throwable>(0));
249
250 /**
251 * The list of suppressed exceptions, as returned by {@link
252 * #getSuppressed()}. The list is initialized to a zero-element
253 * unmodifiable sentinel list. When a serialized Throwable is
254 * read in, if the {@code suppressedExceptions} field points to a
255 * zero-element list, the field is reset to the sentinel value.
256 *
257 * @serial
258 * @since 1.7
259 */
260 private List<Throwable> suppressedExceptions = suppressedSentinel;
261
262 /** Message for trying to suppress a null exception. */
263 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
264
265 /** Message for trying to suppress oneself. */
266 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
267
268 /** Caption for labeling causative exception stack traces */
269 private static final String CAUSE_CAPTION = "Caused by: ";
270
271 /** Caption for labeling suppressed exception stack traces */
272 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
273
274 /**
275 * Constructs a new throwable with {@code null} as its detail message.
276 * The cause is not initialized, and may subsequently be initialized by a
277 * call to {@link #initCause}.
278 *
279 * <p>The {@link #fillInStackTrace()} method is called to initialize
280 * the stack trace data in the newly created throwable.
281 */
282 public Throwable() {
283 fillInStackTrace();
284 }
285
286 /**
287 * Constructs a new throwable with the specified detail message. The
288 * cause is not initialized, and may subsequently be initialized by
289 * a call to {@link #initCause}.
290 *
291 * <p>The {@link #fillInStackTrace()} method is called to initialize
292 * the stack trace data in the newly created throwable.
293 *
294 * @param message the detail message. The detail message is saved for
295 * later retrieval by the {@link #getMessage()} method.
296 */
297 public Throwable(String message) {
298 fillInStackTrace();
299 detailMessage = message;
300 }
301
302 /**
303 * Constructs a new throwable with the specified detail message and
304 * cause. <p>Note that the detail message associated with
305 * {@code cause} is <i>not</i> automatically incorporated in
306 * this throwable's detail message.
307 *
308 * <p>The {@link #fillInStackTrace()} method is called to initialize
309 * the stack trace data in the newly created throwable.
310 *
311 * @param message the detail message (which is saved for later retrieval
312 * by the {@link #getMessage()} method).
313 * @param cause the cause (which is saved for later retrieval by the
314 * {@link #getCause()} method). (A {@code null} value is
315 * permitted, and indicates that the cause is nonexistent or
316 * unknown.)
317 * @since 1.4
318 */
319 public Throwable(String message, Throwable cause) {
320 fillInStackTrace();
321 detailMessage = message;
322 this.cause = cause;
323 }
324
325 /**
326 * Constructs a new throwable with the specified cause and a detail
327 * message of {@code (cause==null ? null : cause.toString())} (which
328 * typically contains the class and detail message of {@code cause}).
329 * This constructor is useful for throwables that are little more than
330 * wrappers for other throwables (for example, {@link
331 * java.security.PrivilegedActionException}).
332 *
333 * <p>The {@link #fillInStackTrace()} method is called to initialize
334 * the stack trace data in the newly created throwable.
335 *
336 * @param cause the cause (which is saved for later retrieval by the
337 * {@link #getCause()} method). (A {@code null} value is
338 * permitted, and indicates that the cause is nonexistent or
339 * unknown.)
340 * @since 1.4
341 */
342 public Throwable(Throwable cause) {
343 fillInStackTrace();
344 detailMessage = (cause==null ? null : cause.toString());
345 this.cause = cause;
346 }
347
348 /**
349 * Returns the detail message string of this throwable.
350 *
351 * @return the detail message string of this {@code Throwable} instance
352 * (which may be {@code null}).
353 */
354 public String getMessage() {
355 return detailMessage;
356 }
357
358 /**
359 * Creates a localized description of this throwable.
360 * Subclasses may override this method in order to produce a
361 * locale-specific message. For subclasses that do not override this
362 * method, the default implementation returns the same result as
363 * {@code getMessage()}.
364 *
365 * @return The localized description of this throwable.
366 * @since JDK1.1
367 */
368 public String getLocalizedMessage() {
369 return getMessage();
370 }
371
372 /**
373 * Returns the cause of this throwable or {@code null} if the
374 * cause is nonexistent or unknown. (The cause is the throwable that
375 * caused this throwable to get thrown.)
376 *
377 * <p>This implementation returns the cause that was supplied via one of
378 * the constructors requiring a {@code Throwable}, or that was set after
379 * creation with the {@link #initCause(Throwable)} method. While it is
380 * typically unnecessary to override this method, a subclass can override
381 * it to return a cause set by some other means. This is appropriate for
382 * a "legacy chained throwable" that predates the addition of chained
383 * exceptions to {@code Throwable}. Note that it is <i>not</i>
384 * necessary to override any of the {@code PrintStackTrace} methods,
385 * all of which invoke the {@code getCause} method to determine the
386 * cause of a throwable.
387 *
388 * @return the cause of this throwable or {@code null} if the
389 * cause is nonexistent or unknown.
390 * @since 1.4
391 */
392 public synchronized Throwable getCause() {
393 return (cause==this ? null : cause);
394 }
395
396 /**
397 * Initializes the <i>cause</i> of this throwable to the specified value.
398 * (The cause is the throwable that caused this throwable to get thrown.)
399 *
400 * <p>This method can be called at most once. It is generally called from
401 * within the constructor, or immediately after creating the
402 * throwable. If this throwable was created
403 * with {@link #Throwable(Throwable)} or
404 * {@link #Throwable(String,Throwable)}, this method cannot be called
405 * even once.
406 *
407 * @param cause the cause (which is saved for later retrieval by the
408 * {@link #getCause()} method). (A {@code null} value is
409 * permitted, and indicates that the cause is nonexistent or
410 * unknown.)
411 * @return a reference to this {@code Throwable} instance.
412 * @throws IllegalArgumentException if {@code cause} is this
413 * throwable. (A throwable cannot be its own cause.)
414 * @throws IllegalStateException if this throwable was
415 * created with {@link #Throwable(Throwable)} or
416 * {@link #Throwable(String,Throwable)}, or this method has already
417 * been called on this throwable.
418 * @since 1.4
419 */
420 public synchronized Throwable initCause(Throwable cause) {
421 if (this.cause != this)
422 throw new IllegalStateException("Can't overwrite cause");
423 if (cause == this)
424 throw new IllegalArgumentException("Self-causation not permitted");
425 this.cause = cause;
426 return this;
427 }
428
429 /**
430 * Returns a short description of this throwable.
431 * The result is the concatenation of:
432 * <ul>
433 * <li> the {@linkplain Class#getName() name} of the class of this object
434 * <li> ": " (a colon and a space)
435 * <li> the result of invoking this object's {@link #getLocalizedMessage}
436 * method
437 * </ul>
438 * If {@code getLocalizedMessage} returns {@code null}, then just
439 * the class name is returned.
440 *
441 * @return a string representation of this throwable.
442 */
443 public String toString() {
444 String s = getClass().getName();
445 String message = getLocalizedMessage();
446 return (message != null) ? (s + ": " + message) : s;
447 }
448
449 /**
450 * Prints this throwable and its backtrace to the
451 * standard error stream. This method prints a stack trace for this
452 * {@code Throwable} object on the error output stream that is
453 * the value of the field {@code System.err}. The first line of
454 * output contains the result of the {@link #toString()} method for
455 * this object. Remaining lines represent data previously recorded by
456 * the method {@link #fillInStackTrace()}. The format of this
457 * information depends on the implementation, but the following
458 * example may be regarded as typical:
459 * <blockquote><pre>
460 * java.lang.NullPointerException
461 * at MyClass.mash(MyClass.java:9)
462 * at MyClass.crunch(MyClass.java:6)
463 * at MyClass.main(MyClass.java:3)
464 * </pre></blockquote>
465 * This example was produced by running the program:
466 * <pre>
467 * class MyClass {
468 * public static void main(String[] args) {
469 * crunch(null);
470 * }
471 * static void crunch(int[] a) {
472 * mash(a);
473 * }
474 * static void mash(int[] b) {
475 * System.out.println(b[0]);
476 * }
477 * }
478 * </pre>
479 * The backtrace for a throwable with an initialized, non-null cause
480 * should generally include the backtrace for the cause. The format
481 * of this information depends on the implementation, but the following
482 * example may be regarded as typical:
483 * <pre>
484 * HighLevelException: MidLevelException: LowLevelException
485 * at Junk.a(Junk.java:13)
486 * at Junk.main(Junk.java:4)
487 * Caused by: MidLevelException: LowLevelException
488 * at Junk.c(Junk.java:23)
489 * at Junk.b(Junk.java:17)
490 * at Junk.a(Junk.java:11)
491 * ... 1 more
492 * Caused by: LowLevelException
493 * at Junk.e(Junk.java:30)
494 * at Junk.d(Junk.java:27)
495 * at Junk.c(Junk.java:21)
496 * ... 3 more
497 * </pre>
498 * Note the presence of lines containing the characters {@code "..."}.
499 * These lines indicate that the remainder of the stack trace for this
500 * exception matches the indicated number of frames from the bottom of the
501 * stack trace of the exception that was caused by this exception (the
502 * "enclosing" exception). This shorthand can greatly reduce the length
503 * of the output in the common case where a wrapped exception is thrown
504 * from same method as the "causative exception" is caught. The above
505 * example was produced by running the program:
506 * <pre>
507 * public class Junk {
508 * public static void main(String args[]) {
509 * try {
510 * a();
511 * } catch(HighLevelException e) {
512 * e.printStackTrace();
513 * }
514 * }
515 * static void a() throws HighLevelException {
516 * try {
517 * b();
518 * } catch(MidLevelException e) {
519 * throw new HighLevelException(e);
520 * }
521 * }
522 * static void b() throws MidLevelException {
523 * c();
524 * }
525 * static void c() throws MidLevelException {
526 * try {
527 * d();
528 * } catch(LowLevelException e) {
529 * throw new MidLevelException(e);
530 * }
531 * }
532 * static void d() throws LowLevelException {
533 * e();
534 * }
535 * static void e() throws LowLevelException {
536 * throw new LowLevelException();
537 * }
538 * }
539 *
540 * class HighLevelException extends Exception {
541 * HighLevelException(Throwable cause) { super(cause); }
542 * }
543 *
544 * class MidLevelException extends Exception {
545 * MidLevelException(Throwable cause) { super(cause); }
546 * }
547 *
548 * class LowLevelException extends Exception {
549 * }
550 * </pre>
551 * As of release 7, the platform supports the notion of
552 * <i>suppressed exceptions</i> (in conjunction with the {@code
553 * try}-with-resources statement). Any exceptions that were
554 * suppressed in order to deliver an exception are printed out
555 * beneath the stack trace. The format of this information
556 * depends on the implementation, but the following example may be
557 * regarded as typical:
558 *
559 * <pre>
560 * Exception in thread "main" java.lang.Exception: Something happened
561 * at Foo.bar(Foo.java:10)
562 * at Foo.main(Foo.java:5)
563 * Suppressed: Resource$CloseFailException: Resource ID = 0
564 * at Resource.close(Resource.java:26)
565 * at Foo.bar(Foo.java:9)
566 * ... 1 more
567 * </pre>
568 * Note that the "... n more" notation is used on suppressed exceptions
569 * just at it is used on causes. Unlike causes, suppressed exceptions are
570 * indented beyond their "containing exceptions."
571 *
572 * <p>An exception can have both a cause and one or more suppressed
573 * exceptions:
574 * <pre>
575 * Exception in thread "main" java.lang.Exception: Main block
576 * at Foo3.main(Foo3.java:7)
577 * Suppressed: Resource$CloseFailException: Resource ID = 2
578 * at Resource.close(Resource.java:26)
579 * at Foo3.main(Foo3.java:5)
580 * Suppressed: Resource$CloseFailException: Resource ID = 1
581 * at Resource.close(Resource.java:26)
582 * at Foo3.main(Foo3.java:5)
583 * Caused by: java.lang.Exception: I did it
584 * at Foo3.main(Foo3.java:8)
585 * </pre>
586 * Likewise, a suppressed exception can have a cause:
587 * <pre>
588 * Exception in thread "main" java.lang.Exception: Main block
589 * at Foo4.main(Foo4.java:6)
590 * Suppressed: Resource2$CloseFailException: Resource ID = 1
591 * at Resource2.close(Resource2.java:20)
592 * at Foo4.main(Foo4.java:5)
593 * Caused by: java.lang.Exception: Rats, you caught me
594 * at Resource2$CloseFailException.<init>(Resource2.java:45)
595 * ... 2 more
596 * </pre>
597 */
598 public void printStackTrace() {
599 printStackTrace(System.err);
600 }
601
602 /**
603 * Prints this throwable and its backtrace to the specified print stream.
604 *
605 * @param s {@code PrintStream} to use for output
606 */
607 public void printStackTrace(PrintStream s) {
608 printStackTrace(new WrappedPrintStream(s));
609 }
610
611 private void printStackTrace(PrintStreamOrWriter s) {
612 // Guard against malicious overrides of Throwable.equals by
613 // using a Set with identity equality semantics.
614 Set<Throwable> dejaVu =
615 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
616 dejaVu.add(this);
617
618 synchronized (s.lock()) {
619 // Print our stack trace
620 s.println(this);
621 StackTraceElement[] trace = getOurStackTrace();
622 for (StackTraceElement traceElement : trace)
623 s.println("\tat " + traceElement);
624
625 // Print suppressed exceptions, if any
626 for (Throwable se : getSuppressed())
627 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
628
629 // Print cause, if any
630 Throwable ourCause = getCause();
631 if (ourCause != null)
632 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
633 }
634 }
635
636 /**
637 * Print our stack trace as an enclosed exception for the specified
638 * stack trace.
639 */
640 private void printEnclosedStackTrace(PrintStreamOrWriter s,
641 StackTraceElement[] enclosingTrace,
642 String caption,
643 String prefix,
644 Set<Throwable> dejaVu) {
645 assert Thread.holdsLock(s.lock());
646 if (dejaVu.contains(this)) {
647 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
648 } else {
649 dejaVu.add(this);
650 // Compute number of frames in common between this and enclosing trace
651 StackTraceElement[] trace = getOurStackTrace();
652 int m = trace.length - 1;
653 int n = enclosingTrace.length - 1;
654 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
655 m--; n--;
656 }
657 int framesInCommon = trace.length - 1 - m;
658
659 // Print our stack trace
660 s.println(prefix + caption + this);
661 for (int i = 0; i <= m; i++)
662 s.println(prefix + "\tat " + trace[i]);
663 if (framesInCommon != 0)
664 s.println(prefix + "\t... " + framesInCommon + " more");
665
666 // Print suppressed exceptions, if any
667 for (Throwable se : getSuppressed())
668 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
669 prefix +"\t", dejaVu);
670
671 // Print cause, if any
672 Throwable ourCause = getCause();
673 if (ourCause != null)
674 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
675 }
676 }
677
678 /**
679 * Prints this throwable and its backtrace to the specified
680 * print writer.
681 *
682 * @param s {@code PrintWriter} to use for output
683 * @since JDK1.1
684 */
685 public void printStackTrace(PrintWriter s) {
686 printStackTrace(new WrappedPrintWriter(s));
687 }
688
689 /**
690 * Wrapper class for PrintStream and PrintWriter to enable a single
691 * implementation of printStackTrace.
692 */
693 private abstract static class PrintStreamOrWriter {
694 /** Returns the object to be locked when using this StreamOrWriter */
695 abstract Object lock();
696
697 /** Prints the specified string as a line on this StreamOrWriter */
698 abstract void println(Object o);
699 }
700
701 private static class WrappedPrintStream extends PrintStreamOrWriter {
702 private final PrintStream printStream;
703
704 WrappedPrintStream(PrintStream printStream) {
705 this.printStream = printStream;
706 }
707
708 Object lock() {
709 return printStream;
710 }
711
712 void println(Object o) {
713 printStream.println(o);
714 }
715 }
716
717 private static class WrappedPrintWriter extends PrintStreamOrWriter {
718 private final PrintWriter printWriter;
719
720 WrappedPrintWriter(PrintWriter printWriter) {
721 this.printWriter = printWriter;
722 }
723
724 Object lock() {
725 return printWriter;
726 }
727
728 void println(Object o) {
729 printWriter.println(o);
730 }
731 }
732
733 /**
734 * Fills in the execution stack trace. This method records within this
735 * {@code Throwable} object information about the current state of
736 * the stack frames for the current thread.
737 *
738 * @return a reference to this {@code Throwable} instance.
739 * @see java.lang.Throwable#printStackTrace()
740 */
741 public synchronized native Throwable fillInStackTrace();
742
743 /**
744 * Provides programmatic access to the stack trace information printed by
745 * {@link #printStackTrace()}. Returns an array of stack trace elements,
746 * each representing one stack frame. The zeroth element of the array
747 * (assuming the array's length is non-zero) represents the top of the
748 * stack, which is the last method invocation in the sequence. Typically,
749 * this is the point at which this throwable was created and thrown.
750 * The last element of the array (assuming the array's length is non-zero)
751 * represents the bottom of the stack, which is the first method invocation
752 * in the sequence.
753 *
754 * <p>Some virtual machines may, under some circumstances, omit one
755 * or more stack frames from the stack trace. In the extreme case,
756 * a virtual machine that has no stack trace information concerning
757 * this throwable is permitted to return a zero-length array from this
758 * method. Generally speaking, the array returned by this method will
759 * contain one element for every frame that would be printed by
760 * {@code printStackTrace}.
761 *
762 * @return an array of stack trace elements representing the stack trace
763 * pertaining to this throwable.
764 * @since 1.4
765 */
766 public StackTraceElement[] getStackTrace() {
767 return getOurStackTrace().clone();
768 }
769
770 private synchronized StackTraceElement[] getOurStackTrace() {
771 // Initialize stack trace if this is the first call to this method
772 if (stackTrace == EMPTY_STACK) {
773 int depth = getStackTraceDepth();
774 stackTrace = new StackTraceElement[depth];
775 for (int i=0; i < depth; i++)
776 stackTrace[i] = getStackTraceElement(i);
777 } else if (stackTrace == null) {
778 return EMPTY_STACK;
779 }
780
781 return stackTrace;
782 }
783
784 /**
785 * Sets the stack trace elements that will be returned by
786 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
787 * and related methods.
788 *
789 * This method, which is designed for use by RPC frameworks and other
790 * advanced systems, allows the client to override the default
791 * stack trace that is either generated by {@link #fillInStackTrace()}
792 * when a throwable is constructed or deserialized when a throwable is
793 * read from a serialization stream.
794 *
795 * <p>If the stack trace is set to one-element array containing
796 * the {@linkplain #STACK_TRACE_ELEMENT_SENTINEL stack trace sentinel}
797 * value, then future calls to this method have no effect other
798 * than validating the argument is non-null.
799 *
800 * @param stackTrace the stack trace elements to be associated with
801 * this {@code Throwable}. The specified array is copied by this
802 * call; changes in the specified array after the method invocation
803 * returns will have no affect on this {@code Throwable}'s stack
804 * trace.
805 *
806 * @throws NullPointerException if {@code stackTrace} is
807 * {@code null}, or if any of the elements of
808 * {@code stackTrace} are {@code null}
809 *
810 * @since 1.4
811 */
812 public void setStackTrace(StackTraceElement[] stackTrace) {
813 // Null-check the argument
814 StackTraceElement[] defensiveCopy = stackTrace.clone();
815
816 if (stackTrace == null)
817 return;
818
819 if (defensiveCopy.length == 1 &&
820 STACK_TRACE_ELEMENT_SENTINEL.equals(defensiveCopy[0]))
821 defensiveCopy = null;
822 else {
823 for (int i = 0; i < defensiveCopy.length; i++)
824 if (defensiveCopy[i] == null)
825 throw new NullPointerException("stackTrace[" + i + "]");
826 }
827
828 synchronized (this) {
829 this.stackTrace = defensiveCopy;
830 }
831 }
832
833 /**
834 * Returns the number of elements in the stack trace (or 0 if the stack
835 * trace is unavailable).
836 *
837 * package-protection for use by SharedSecrets.
838 */
839 native int getStackTraceDepth();
840
841 /**
842 * Returns the specified element of the stack trace.
843 *
844 * package-protection for use by SharedSecrets.
845 *
846 * @param index index of the element to return.
847 * @throws IndexOutOfBoundsException if {@code index < 0 ||
848 * index >= getStackTraceDepth() }
849 */
850 native StackTraceElement getStackTraceElement(int index);
851
852 /**
853 * Read a {@code Throwable} from a stream, enforcing
854 * well-formedness constraints on fields. Null entries and
855 * self-pointers are not allowed in the list of {@code
856 * suppressedExceptions}. Null entries are not allowed for stack
857 * trace elements. A single-element stack trace whose entry is
858 * equal to {@link #STACK_TRACE_ELEMENT_SENTINEL} results in a
859 * {@code null} {@code stackTrace} field.
860 *
861 * Note that there are no constraints on the value the {@code
862 * cause} field can hold; both {@code null} and this are valid
863 * values for the field.
864 */
865 private void readObject(ObjectInputStream s)
866 throws IOException, ClassNotFoundException {
867 s.defaultReadObject(); // read in all fields
868 List<Throwable> suppressed = null;
869 if (suppressedExceptions != null &&
870 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
871 suppressed = new ArrayList<Throwable>(1);
872 for (Throwable t : suppressedExceptions) {
873 // Enforce constraints on suppressed exceptions in
874 // case of corrupt or malicious stream.
875 if (t == null)
876 throw new NullPointerException(NULL_CAUSE_MESSAGE);
877 if (t == this)
878 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
879 suppressed.add(t);
880 }
881 }
882
883 // If suppressed is a zero-length list, use the sentinel
884 // value.
885 if (suppressed != null && suppressed.isEmpty())
886 suppressedExceptions = suppressedSentinel;
887 else
888 suppressedExceptions = suppressed;
889
890 // Check for the marker for an immutable stack trace
891 if (stackTrace != null) {
892 // Share zero-length stack traces
893 if (stackTrace.length == 0) {
894 stackTrace = EMPTY_STACK;
895 } else if (stackTrace.length == 1 &&
896 STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
897 stackTrace = null;
898 } else { // Verify stack trace elements are non-null.
899 for(StackTraceElement ste : stackTrace) {
900 if (ste == null)
901 throw new NullPointerException("null StackTraceElement in serial stream. ");
902 }
903 }
904 }
905
906 // A null stackTrace field in the serial form can result from
907 // an exception serialied without that field. Such exceptions
908 // are now treated as having immutable stack traces.
909 }
910
911 /**
912 * Write a {@code Throwable} object to a stream. A {@code null}
913 * stack trace field is represented in the serial form as a
914 * one-element array whose element is equals to {@link
915 * #STACK_TRACE_ELEMENT_SENTINEL}.
916 */
917 private synchronized void writeObject(ObjectOutputStream s)
918 throws IOException {
919 // Ensure that the stackTrace field is initialized to a
920 // non-null value, if appropriate. As of JDK 7, a null stack
921 // trace field is a valid value indicating the stack trace
922 // should not be set.
923 getOurStackTrace();
924 ObjectOutputStream.PutField fields = s.putFields();
925
926 fields.put("detailMessage", detailMessage);
927 fields.put("cause", cause);
928 // Serialize a null stacktrace using the stack trace sentinel.
929 if (stackTrace == null)
930 fields.put("stackTrace", STACK_TRACE_SENTINEL);
931 else
932 fields.put("stackTrace", stackTrace);
933 fields.put("suppressedExceptions", suppressedExceptions);
934
935 s.writeFields();
936 }
937
938 /**
939 * Adds the specified exception to the list of exceptions that
940 * were suppressed, typically by the {@code try}-with-resources
941 * statement, in order to deliver this exception.
942 *
943 * If the first exception to be suppressed is {@code null}, that
944 * indicates suppressed exception information will <em>not</em> be
945 * recorded for this exception. Subsequent calls to this method
946 * will not record any suppressed exceptions. Otherwise,
947 * attempting to suppress {@code null} after an exception has
948 * already been successfully suppressed results in a {@code
949 * NullPointerException}.
950 *
951 * <p>Note that when one exception {@linkplain
952 * #initCause(Throwable) causes} another exception, the first
953 * exception is usually caught and then the second exception is
954 * thrown in response. In contrast, when one exception suppresses
955 * another, two exceptions are thrown in sibling code blocks, such
956 * as in a {@code try} block and in its {@code finally} block, and
957 * control flow can only continue with one exception so the second
958 * is recorded as a suppressed exception of the first.
959 *
960 * @param exception the exception to be added to the list of
961 * suppressed exceptions
962 * @throws IllegalArgumentException if {@code exception} is this
963 * throwable; a throwable cannot suppress itself.
964 * @throws NullPointerException if {@code exception} is null and
965 * an exception has already been suppressed by this exception
966 * @since 1.7
967 */
968 public synchronized void addSuppressed(Throwable exception) {
969 if (exception == this)
970 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
971
972 if (exception == null) {
973 if (suppressedExceptions == suppressedSentinel) {
974 suppressedExceptions = null; // No suppression information recorded
975 return;
976 } else
977 throw new NullPointerException(NULL_CAUSE_MESSAGE);
978 } else {
979 assert exception != null && exception != this;
980
981 if (suppressedExceptions == null) // Suppressed exceptions not recorded
982 return;
983
984 if (suppressedExceptions == suppressedSentinel)
985 suppressedExceptions = new ArrayList<Throwable>(1);
986
987 assert suppressedExceptions != suppressedSentinel;
988
989 suppressedExceptions.add(exception);
990 }
991 }
992
993 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
994
995 /**
996 * Returns an array containing all of the exceptions that were
997 * suppressed, typically by the {@code try}-with-resources
998 * statement, in order to deliver this exception.
999 *
1000 * If no exceptions were suppressed, an empty array is returned.
1001 *
1002 * @return an array containing all of the exceptions that were
1003 * suppressed to deliver this exception.
1004 * @since 1.7
1005 */
1006 public synchronized Throwable[] getSuppressed() {
1007 if (suppressedExceptions == suppressedSentinel ||
1008 suppressedExceptions == null)
1009 return EMPTY_THROWABLE_ARRAY;
1010 else
1011 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1012 }
1013 }